Electric counting circuits



p 1957 G. T. BAKER ETAL 2,805,363

ELECTRIC COUNTING CIRCUITS Filed Aug. 9, 1955 FIGJ.

+5ov +50v +50v W HI HI Hl HI- +50V W2 W3 -y 4 FIG.3.

United States Patent 2,805,363 Patented Sept. 3, 1957 ice George ThomasBaker, deceased, Taplow, and Wincenty Bezdel, London, England, assignorsto British Telecommunications Research Limited, Taplow, England, aBritish company Application August 9, 1955, Serial No. 527,386

Claims priority, application Great Britain August 11, 1954 4 Claims.(Cl. 315-345) The present invention relates to electrical countingcircuits and is more particularly concerned with binary countingcircuits employing gas-filled discharge tubes of the cold-cathode typeas counting elements. Such circuits are known in which a stage in abinary counter comprises two gas discharge tubes arranged in a bi-stabletrigger circuit. In such a circuit, an input pulse extinguishes theconducting tube of the pair and strikes the non-conducting tube. If theoutput is taken in the form of unidirectional pulses from one tube ofthe pair, the output will have half the frequency of the input.

It is the object of the invention to provide an improved binary ccuntingcircuit of the general type mentioned above, which employs a smallernumber of components than existing circuits. According to the invention,a single-stage binary counting circuit comprises a gas-filled dischargetube of the cold-cathode type adapted to be connected in circuit withresistors and capacitors of such value that it is rendered alternatelyconducting and non-conducting by the application of successive similarvoltage impulses to one electrode.

The invention will be better understood from the following descriptionof a preferred form which should be taken in conjunction with theaccompanying drawings, comprising Figs. 1-3. Of these,

Fig. 1 shows a single-stage binary counting element in accordance withthe invention;

Fig. 2 shows the waveform of the output of the counting element, and

Fig. 3 shows a multi-stage binary counting circuit employing a pluralityof the elements shown in Fig. 1.

Referring to Fig. 1, VK is a gas-filled discharge tube of thecold-cathode type, arranged as a binary counting element or frequencyhalver. The anode resistor R1, the anode capacitor C2 and the cathoderesistor R2 are chosen so that (a) they do not form a self-quenchingcircuit, (b) the value of resistor R1 is very much greater than that ofresistor R2, and (c) the combination of resistor R2 and capacitor C2provides an output pulse of suitable shape. The component valuesnecessary to satisfy these conditions will vary somewhat for difierenttubes but satisfactory results have been obtained with R1=68(),0O0 ohms,R2=l5,000 ohms and C2=.01 mfd. The H. T. supply is arranged to have avalue between the breakdown and maintaining voltages for the tube and200 volts was found suitable with the figures pust mentioned.

The tube is controlled via leads and 11. By way of lead it) and resistorR3 a biasing potential is applied to the trigger electrode of the tube.The biasing potential may remain steady or be a controlling waveform,such as a train of rectangular pulses, in which the maximum value of thepotential is just too low to ignite the trigger gap. By way of lead 11and capacitor C1 steepfronted driving pulses are also applied to thetrigger electrode. The sum of the pulse potential and the maximum valueof the bias potential is high enough to ignite the trigger gap.

The operation is as follows. Assume the tube to be in the non-conductingstate and lead 10 to be appropriately biased. A suitable positive pulseapplied at lead 11 will cause the trigger gap to conduct, and ionisationof the tube will take place. Capacitor C2, which is already charged tothe value of the H. T. supply, will now discharge through the tube.

Reference should now be made to Fig. 2 which shows the output waveformappearing at lead 12. At point a the cathode of the tube is at earthpotential when the tube is non-conducting. Point b shows the rapidincrease of cathode voltage as capacitor C2 commences to dischargethrough the tube and cathode resistor R2. The discharge currentdiminishes until it is substantially zero and hence the current throughthe tube is that through resistor R1 only. Because the value of resistorR1 is so much greater than that of resistor R2, the output voltage atthis stage is very small indeed and is indicated by c in Fig. 2.

A second pulse of the same polarity and shape as the first may now beapplied to lead 11. The effect of raising the potential of the triggerelectrode in a tube in which the current is very small is to transferenough ionisation from the main gap to the minor gap so that when theinput pulse has passed the tube is left in a feebly ionised state notsufiicient to maintain the main gap discharge with the voltage retainedon capacitor C2 and is thus extinguished. Because the H. T. supply islower than the breakdown voltage of the main gap, the tube will remainextinguished. Accordingly on receipt of a second input pulse, thecathode potential will return to that of earth, as indicated at point a,and remain in that condition during the period e until a further pulseis applied to the tube.

During the period c between the first and second input pulses, the anodeof the tube is maintained at a potential just greater than the voltagedrop in the tube. During period e, the anode assumes the potential ofthe H. T. supply, as capacitor C2 is able to charge through resistor R1.A third input pulse will now find the circuit in the same condition asdid the first pulse, and the same sequence will be repeated forsubsequent pulses.

it will be seen that the output pulse frequency is half the input pulsefrequency, and the output comprises steep-fronted pulses, b, 7 and soon, as shown in Fig. 2.

In the four-stage binary counting circuit shown in Fig. 3, each stagecomprises a binary element of the type shown in Fig. 1. The last threestages each have their input circuit connected to the output circuit ofthe previous stage, and each tube is continuously primed by connectionof a suitable positive voltage shown as 50 volts, to its triggerelectrode. The input pulses are applied to tube VKl via lead 13, andpulses are passed from stage to stage at a diminishing frequency, eachstage introducing a division by two. In a normal fourstage binarycounter, the total count is sixteen, i. e. after sixteen input pulsesthe pattern of conducting tubes reverts to that existing initially.

A count of sixteen is seldom required in practice, and a more frequentrequirement is a count of ten or twelve. These are readily obtained byintroducing a simple feedback circuit. The counter shown in Fig. 3 isarranged to provide one way of counting ten. From the anode of tube VK4,feedback paths extend to the cathodes of tubes VK2 and VK3 viacapacitors C3 and C4 respectively. Negative pulses will therefore beapplied to the cathodes of tubes VK2 and VK3 when tube VK4 is struck.These negative pulses are only slightly delayed with respect to thepositive cathode pulses occurring at the cathodes of tubes VKZ and VK3and cause extra current "through the tubes resulting in the lowering oftheir anode potentials below the extinction potential. Thus when tubeVK4 ignites tubes VK2 and VK3' are extinguished. The pattern ofconducting. tubes, there.- fore, 'will'n'otp'roceed in a regular manner,and the-count will, in fact, be reduced to ten conditions.

'The pattern of fired tubes 'in each of the ten stages is asjfollow's, 0indicating a non-conducting tube and l a conducting tube:

VKl VK2 V K3 VK4 1 -0 O 0 0 0 l 1 1 1 0 0 -1 1 O 1 0 1 0 0 0 1 0 1 1 0 O(l 1 0 O 1 0 0 0 O O 0 0 1 1 1 1 which immediately changes to We claim:

I. A 'single stage binary counting circuit comprising a single coldcathode gas discharge tube in association with a capacitor and at leasttwo resistors, the values of said capacitor and resistors being sochosen that a suitable pulse applied to the trigger electrode causes thetube to strike and continue to pass current after the pulse ceases butof a much smaller value and on the subsequent application of a similarpulse to the trigger electrode the tube isextinguished when the pulseceases.

2. A single-stage binary counting circuit employing a cold cathode gasdischarge tube in which the trigger electrode of the tube is connectedto a biassing or priming potential over a resistor and is supplied withinput pulses by way of a capacitor, the main discharge path includingresistors connected respectively to the anode and cathode, the anoderesistor being large compared with the cathode resistor and a capacitorbeing connected between the anode and the negative pole of the sourceand the output being taken from the cathode, the values of the differentcomponents being so chosen that the tube is rendered alternatelyconducting and non-conducting by the application of successive similarinput pulses to the trigger electrode.

'3. A counting circuit as claimed in claim 2 in which the biassingpotential is supplied in the form of pulses.

4. A decimal counting circuit employing four singlesta-ge circuits asclaimed in claim 2 in which the required operation is secured byproviding feedback from the final stage to the second and third stages.

References 'Citedin the file of this patent UNITED STATES PATENTS

